By directing the easy axis of magnetization of the magnetic recording layer that was conventionally directed in the in-plane direction of the medium, the demagnetizing field near the magnetic transition region, which is the boundary between recording bits, becomes smaller. As a result, the static magnetism stabilizes with the increase in recording density, and the resistance to thermal fluctuation improves, therefore, the perpendicular magnetic recording system is a suitable system for enhancing surface recording density.
When a soft magnetic underlayer made of soft magnetic material is provided between the substrate and the perpendicular magnetic recording layer, it works as the so-called vertical two-layer medium, and high recording performance can be obtained. In this condition, the soft magnetic underlayer has the role of refluxing the recording magnetic field from the magnetic head, and thus enhancing the recording and reproducing efficiency.
Amorphous materials such as CoZrNb, CoTaZr, and FeCoB are generally proposed as soft magnetic material for forming the soft magnetic underlayer mentioned above. For instance, CoZr alloy (refer to Patent Document 1) or FeAlSi, FeTaN (refer to Patent Document 2) may be used. Various kinds of materials have been proposed for the under layer to be provided on the soft magnetic underlayer mentioned above. For instance, hcp structures such as Ti alloy (refer to Patent Document 3) and NiFeCr (refer to Patent Document 4) or amorphous structures such as Ta may be used.
If CoZrNb or CoTaZr is used as the soft magnetic underlayer mentioned above, the problem of corrosion of Co or Fe at high temperature and high humidity occurs in CoFe alloys in both kinds of materials. It has been observed that in CoFe alloy with Fe added thereto to increase the saturation magnetic flux density (Bs), this problem is more noticeable.
If a material with no magnetism in the under layer is used, the distance of the head and soft magnetic underlayer surface increases further from the thickness of the under layer, and the soft magnetic underlayer has to be increased in thickness to enable adequate writes. By using material with soft magnetic characteristics in the under layer, both the role of the soft magnetic underlayer and the crystal orientation of the intermediate layers provided above can be controlled. However, it has been observed that when Ni, Ni alloy, NiFe alloy or NiCo alloy materials are used in the under layer, the crystal orientation changes significantly depending on the soft magnetic underlayer material.
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. H6-282834.
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. H11-149628.
Patent Document 3: Japanese Patent Publication No. 2669529.
Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2003-123239.